98 LIVERPOOL BIOLOGICAL SOCIETY. 
(b) The tentacular canals. 
(c) A canal parallel to (a), and apparently empty. 
The large canals (a) and (c) have no communication 
with one another, except so far as they both open into a 
system of lacune in the cesophageal region. 
Nerves.—With regard to the nervous system, I must 
refer to M. Joubin’s paper. He advises staining the tissue 
to be observed with methyl green and borax carmine, 
making transparent with glycerine, and subjecting to 
pressure. This method he considers preferable to the 
observation of sections, the results appearing to him more 
satisfactory. After giving some account of the nervous 
system in general, he describes as a ganglionic plexus a 
system of nerves and nerve cells running throughout the 
length of the arms parallel to the large canal containing 
the brachial muscle, and giving off nerves in many direc- 
tions, but especially to certain regions of the fold and 
tentacles, where the epithelium is seen to be deeper than 
elsewhere. 
THE TISSUES. 
There are two systems of tissue which call for special 
notice ; these are the epithelial and sub-epithelial tissues. 
The sub-epithelial tisswe is remarkably constant in 
structure throughout the whole body, but its development 
in thickness is extremely varied; it may be a very thin 
and fine plate, as in the greater part of the alimentary 
canal; or it may be thick, firm and elastic, as in the arms 
(see Pl. III., figs. 2 and 3). It is continuous in the arms, 
mantle, body-wall, alimentary canal, “‘liver,’”’? and mesen- 
tery (see Pl. IV., fig. 1), and a tissue not distinguishable 
from it forms, what for want of a better name I must call, 
the muscle terminations; this last seems to be the only 
case where this tissue is not continuous, it occurs as a 
